Power has been called many things. The ultimate aphrodisiac. An absolute corrupter. A mistress. A musical instrument. But its true nature remains elusive. After all, a head of state wields a very different sort of power than a religious figure. Can one really compare the influence of a journalist with that of a terrorist? And is power unexercised power at all? In compiling our first ranking of the World's Most Powerful People, we wrestled with these questions--and many more--before deciding to define power by four dimensions. First, do they have influence over lots of other people? Do they control relatively large financial resources compared with their peers? Are they powerful in multiple spheres? There are only 67 slots on our list--one for every 100 million people on the planet--so being powerful in just one area is not enough. Lastly, we insisted that our choices actively use their power